Here is another way to develop a thesis:

Step 1: Ask a specific question about the text.
Step 2: Answer the specific question about the text (this becomes your thesis).

1. To what extent is Macbeth influenced by the influence of other characters, and is there a pattern in this?

2. Macbeth is influenced whenever he is in a situation where he is under pressure or belittled, perhaps signifying the feebleness of the human mind and its indecisiveness.